I really liked the mage-tech angle for Old Ekkremes I saw in Jacob Munford's round 2 pitch. Here I wanted to show the other side: the people who are embracing this primal upwelling of mana as Ekkremes enters a new age. I included my full draft below, I'd love to hear what people think of the direction and mechanics.

Set: Ekkremes

Pitch Name: Embrace the age of mana

Mechanical Themes: Sunburst, Monocolor Hybrid, Operate/Artifacts

50 Words:
Sunburst is primarily Red and Green, and represents the shift from a mana-poor to a mana-rich age on Ekkremes. Sunburst is supported with Red mana filtering (see Fire Weaver, a colorshifted Orochi Leafcaller) and Green ramp, providing a counterpoint to the technotopia colorless/artifact theme in Blue, Black, and White.

Energy Channeler 4R
Creature - Goblin Shaman
Whenever you cast a creature spell, ~ deals X damage to target creature, where X is the number of colors of mana spent to cast that spell.
2/3

Power Plant 2
Artifact
Operate 2 (2: Attach an unattached creature you control to this artifact, or unattach a creature from it. An attached creature can't attack or block. Operate only as a sorcery.)
T: Add 1 or one mana of any color to your mana pool for each creature attached to ~.

50 Word Summary:
Sunburst, representing Ekkremes's reemergence of mana, appears in all colors but is focused in Green and Red, with Red getting one-shot mana filtering to support it. Monocolor-Hybrid and colorless-matters (all colors, but mostly Blue/Black/White) represent the technotopia that dominated a mana-poor world. Smoothing mechanic Bulldoze supports both multicolor and colorless.

Militant Mystic 2R
Creature - Human WizardSunburst - ~ enters the battlefield with a +1/+1 counter on it for each color of mana spent to cast it.
First strike
0/0

Demolition Crew {2/R}{2/R}
Artifact Creature - Human MutantBulldoze - When ~ enters the battlefield, you may sacrifice a land. If you do, search your library for a basic land card or a Building card and put it onto the battlefield tapped. Then shuffle your library.
2/2

Solar Flare 2R
InstantSunburst - Creatures you control get +1/+0 until end of turn for each color of mana spent to cast ~.

Power Plant 2
Artifact
Operate 1 (1: Attach an unattached creature you control to this artifact, or unattach a creature from it. An attached creature can't attack or block. Operate only as a sorcery.)
T: add 1 to your mana pool. If a creature is operating ~, add one mana of any color to your mana pool instead.

Factory Explosion 2R
Instant
Destroy target artifact. If any creatures were operating that artifact, ~ deals 2 damage to each of those creatures.

Fire Weaver: I don't like color fixing bleeding to red. Solid, though.Mana-Infused Warrior: This is a solid, simple card. Is Ekkremes pushing toward a five color theme, however? Also, name is really bland.Demolition Crew: I can see Ekkremes moving toward five color with this card. I don't like the dual split of add one or any color. Why would you add 1? You would add one mana of any color any time. This is also quite powerful without a tap trigger. I would add a tap trigger.Energy Channeler: Not at common. This is fine, but I'm worried about players having to count their mana every time they activate this ability.Power Plant: Why isn't this Springleaf Drum?Factory Explosion: At worst, this is a worse Shatter. Seems fine, though I would lower the damage from 3 to 2 simply because blowout potential on commons are bad.

red/green hybrid has Wild Cantor, Manamorphose, and Morselhoarder which can add mana of any color, and Smokebraider can add two mana of any color limited to Elemental spells, so there is some limited precedent for the ability. I think it's important to look out for abilities that make sense at Red Common that aren't just dealing damage, and mana filtering makes thematic sense, playing up Red's artistic side. But it's possible Red Orochi Leafcaller is too much.

Some alternate Fire Weavers that don't step quite so much on Green's toes:

Now that you mention it, Energy Channeler should definitely trigger off of instants/sorceries instead of creatures. Pseudo-sunburst for instants and sorceries is perfect.

Factory Explosion was modeled after Unforge from Darksteel, but I agree it would probably be fine at 1R. My thinking was that costing it more conservatively at 2R makes it more of a sideboard card, and thus lets Operate shine more in draft.

Factory Explosion was modeled after Unforge from Darksteel, but I agree it would probably be fine at 1R. My thinking was that costing it more conservatively at 2R makes it more of a sideboard card, and thus lets Operate shine more in draft.

Maybe 2 damage is appropriate as suggested by Prophylaxis. This is different from Unforge though, in that attached creatures are not able to attack or block anyway (unlike the creature damaged by Unforge).

How many players will understand the difference between Factory Explosion and Unforge/Turn to Slag? Does Operate need to reverse the direction of attachment?

I would love to see Sunburst return and on colored spells. Mana-Infused Warrior is pretty sweet. Energy Channeler is quite nice too.

Fireweaver and Demolition Crew are definitely pushing the color pie pretty hard. The set could justify it, but even then I'd expect a limit to how much you can do it. Either making it a tap ability or making it deal 1 damage to you whenever you do it.

Thanks everyone for the feedback. Seems like Red mana filtering is more controversial than I thought. It's probably not wise to give Red permanent mana filtering like my colorshifted Orochi Leafcaller. Now that I think about it more, one-shot filtering effects, like Filtering Akki Rockspeaker below, seem like less egregious color pie violations, but I'd be interested to hear what people think.

I'm envisioning an Ekkremes in which white, blue, and black focus primarily on artifacts and colorless matters, while green and red focus primarily on multicolor/sunburst; red seemed the most natural candidate for sunburst after green.

Blue Colorless Matters {2/U}{2/U}
Artifact Creature - Mutant
Flying
If only colorless mana was spent to cast ~, it enters the battlefield with a +1/+1 counter on it.
2/1

Energy Channeler fits the recent mold of Red Uncommon that supports the set's mechanic (Pyroconvergence, Rumbling Aftershocks, Burning Vengeance, etc.), and so probably shouldn't be common. I can see a green counterpoint that gives all your creatures sunburst, especially after changing the Red one to trigger off only instants and sorceries.

Demolition Crew was designed to support both sunburst and colorless matters, but in a vacuum it seems like it could be a confusing card. It should probably be changed to only add colorless mana. It might not have a home in this submission after that change.

Power Plant does compare unfavorably to Springleaf Drum. This version should feel more distinct:

Power Plant 2
Artifact
Operate 1 (1: Attach an unattached creature you control to this artifact, or unattach a creature from it. An attached creature can't attack or block. Operate only as a sorcery.)
T: add 1 to your mana pool. If a creature is operating ~, add one mana of any color to your mana pool instead.

The confusability with Factory Explosion and equipment could be avoided by giving Operable artifacts a subtype like "contraption" and restricting Factory Explosion to that subtype. It becomes a narrower card, but that might not be a bad thing.

Thanks again for everyone's comments, this is much better than designing in a vacuum.

These are great ideas. I like the Operate that can accept many Operators.

Mono-color vs. Many-color is a great idea. I think it would work best if the set has a dual structure like Kamigawa, and each color gets some cards for mono-color decks and some cards for multi-color decks (hopefully with a decent number of overlap cards as well). I think Multicolor is best when you can actually combine colors as you please rather than when you're forced to work with a particular color combination as the base. Monocolor has the risk of being monotonous, so there should 5 versions of them, one for each color.

There should be some kind of supporting mechanic like Basic Landcycling to help out the theme. Maybe something like:
Mana upheaval (Sacrifice a land you control. If you do, reveal cards from the top of your library until you reveal a land card with a different name and put it onto the battlefield, tapped. Put the remaining cards on the bottom of your library at random.)

It could be used by a mono-color decks with a minor secondary color if you draw too many lands in your minor color, or by multicolor decks to fix your lands. However, the text is probably too long to go on a lot of cards.

I wish there could be Mages that gain charge counters with Sunburst rather than +1/+1 counters. They could use the charge counters for their activated abilities.

If we just go with ordinary Sunburst, I guess we could have enchantments with Sunburst that gain charge counters.

I wish we could put Sunburst on Instants and Sorceries, to represent that it's about Magic and not Artifice this time, so maybe it should be a new version of Sunburst, the way Infect is a new version of Wither. What kind of counters could Instants and Sorceries on the stack use? Or maybe it copies itself for each color used?

For mana filtering effects in Red, I think sticking to one-shot effects would help it feel different. There could be a new volcano-like "charge and release" style for Red:

T, Return a land you control to your hand: Add one mana of any color to your mana pool.

Factory Explosion could say "it deals damage to each creature equipping or operating that artifact." It looks really strong in a set full of artifact creatures, it could cost even more. I wouldn't want to overpunish people who try to make use of the operate mechanic with multiple creatures too much, though, so maybe it should only deal 1 damage.

Colorless matters guy seems sweet, but where are we going to get that much colorless mana? Would it be sufficient to say, "if you paid the maximum cost to cast ~"?

Maybe green can produce any color of mana and red can produce Jund colors. (B, R or G)

Specifying "equipping" or "operating" eliminates the confusion for Factory Explosion quite nicely, though it does mean players could still be confused when they Unforge a Power Plant. In fairness, that's not something likely to come up in actual play, and more of a Melvin-only hypothetical.

It's probably wise to let all colors play with sunburst and monocolor, but I think each color should support the two to different degrees: If Green and Red support sunburst more than monocolor/colorless, Blue would support monocolor/colorless more than sunburst, etc.

Supporting colorless is tough. Wizards did it once, in Masters Edition IV, by putting an Urza's land in each booster. If you picked up lots of Urza lands, you had your pick of 7-drop artifacts to fill out your deck, and you could draft a real X/artifact deck, with something like 7 basic lands and 10 urza lands. I don't think that kind of approach would be ideal for this set. We could add a sixth basic land, but that brings its own headaches. Maybe just "if you paid any colorless mana to cast this".